Metilglioksal'ın (MG) Arabidopsis thaliana'da Azot Metabolizması ve Glioksalaz Sistemi Üzerine Etkileri

Methylglyoxal

(MG), a high-level

reactive carbonyl compound and a powerful oxidant is a mutagenic and cytotoxic

intermediate that can induce DNA breakdown and point mutations, but at the same

time causing Advanced Glycation End Products (AGE’s). MG is also known to

disrupt glucose metabolism, which leads to intracellular ATP depletion and

mitochondrial dysfunctions Kaur et al. 2014). MG in the cells is produced

during enzymatic and non-enzymatic elimination of inorganic phosphate (Pi),

especially under stressful conditions, from glycolytic intermediates including

dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. Other sources of

intracellular MG include catabolism of carbohydrate, lipid, and nitrogenous

compounds (such as proteins). Almost all live systems, including plants, have

glyoxalase systems in cells to counteract the increased MG toxicity under stressful

conditions. The glyoxalase system is mainly composed of two enzymes, Glyoxalase-I

(Gly-I) and Glyoxalase-II (Gly-II). Gly-I converts MG to S-lactoylglutathion

(SLG) by using reduced glutathione (GSH). The S-lactoylglutathione formed here

is converted by GLY-II into D-lactate and GSH (Hossain et al., 2009; Kaur et al., 2014). Thus,

MG is scavenging in the cells.<o:p></o:p>

Although MG toxicity, which was discovered about

eighty years ago, has been studied extensively in animal organisms, very few

studies have been conducted on plants. For this reason, biochemical and

physiological responses to both exogenous and endogenous MG accumulation in

plants are still very unclear. It is believed that the primary role of this

system is the detoxification of the MG toxin. However, the identification of isoforms

of the enzymes in the system that are catalytic to other substrates from known

substrates (MG and SLG) suggests that the glyoxalase system can play another

additional role. The increase of glyoxalase expression in biotic and abiotic

stress response conditions, and consequently the overexpression of enzymes of

which as a resulting the increased stress tolerance of plants strengthen these

approaches. The glyoxalase system is found in almost every organism, including

plants, and the organism is expressed in all tissues. This manifests the

importance of the glyoxalase system but also shows why it is important to work

on it (Thornalley,

1990; Kalapos, 1999).<o:p></o:p>

In our project, the relationship between the

glyoxalase system and nitrogen metabolism became intense. Because, nitrogen

metabolism is regulated by complex mechanisms to optimize the growth of plants,

and plays an important role during the period of germination, vegetative and

generative growth-development. In this situation, In our work, the following

were the questions that were primarily addressed: What are the direct roles of

MG on the enzymes of the glyoxalase system, which are exogenously applied to a

plant? What are the effects of exogenous MG on the enzymes of plant nitrogen

metabolism (nitrate reductase, nitrite reductase, glutamate synthase, and

glutamine synthase)? Is there a relationship between the glyoxalase system and

nitrogen metabolism in the response to MG toxicity? There is significant

disunity in the literature on these issues. In our work, to resolve these

questions, we will use tools to determine the effects

of MG administration on both gene expression levels and enzymatic activity

levels of the enzymes involved in both systems (glyoxalase and nitrogen

metabolism) in the Arabidopsis thaliana,

a model organism. The findings are expected to reveal the effects of MG on

nitrogen metabolism in plants and to explain the relationship between nitrogen

metabolism and glyoxalase systems. In addition, our findings will contribute

significantly to reducing the toxicity of MG, which increases in almost all

stress conditions and the regulation of stress response in plants.<o:p></o:p>